The invention relates to a dryer with an integrated cooling unit and, more particularly, wherein the cooling unit is disposed downline of a web-processing rotary printing machine; and a method of operating the dryer.
U.S. Pat. No. 5,471,847 discloses a web cooling device. With the improvement disclosed therein, the disadvantages of previous drying concepts are sought to be overcome by is providing for the web to be cooled primarily by the evaporation of a liquid instead of by thermal conduction or convection. In this regard, sufficient moisture remains in the web so that shrinkage of the web does not occur, and static charging of the web is at a minimum. In a dryer for offset printing applications, the web is dried down to 2% residual moisture content and thereby absorbs moisture in an amount leading up to a moisture content of between 4% and 6% from the air surrounding it. This additional moisture uptake from the surroundings is implemented, in accordance with the foregoing U.S. patent, by a moisture application device provided specifically for this purpose.
The published European Patent Document EP 0 723 126 A1 discloses a control device and an arrangement for a drying process performed continuously in an industrial dryer. In a flotation dryer wherein a material web is floatingly guided for drying the web in stages, solvent-containing air recirculates in the interior of the dryer. A method is proposed for improving the control of the solvent-containing air in the interior of the dryer. Condensation of the solvents and various by-products based upon solvents are thereby significantly reduced or even eliminated altogether. By the method disclosed in this reference, not only can a considerable reduction in condensation be achieved, but also more intensive mixing and hence more uniform distribution of the solvents, due to which the safety level as a whole is raised, in the regions wherein solvent-containing air is present in which concentrations are avoided entirely. Ambient air passes into the dryer and is mixed with the solvent-containing air in the interior of the dryer. The air mixture is fed back to the first zone of the dryer in accordance with this European patent document. As a result, the open flame of the burner is cooled from the outside by ambient air. After the open flame has been cooled by ambient air, recirculated air from the interior of the dryer is mixed with the fresh air. In the improved process described in the European patent document, the volume of the exhaust gas passing to a recombustion unit that may be present is not reduced significantly. In the disclosed embodiment, ambient air is employed for the purpose of cooling the open burner flame and of eliminating undesired compounds of organic volatile constituents. In the improvement according to this European patent document, the residence time of the combustion mixture in the burner unit appears to be dimensioned inadequately.
The published German Patent Document DE 32 07 461 A1 is concerned with a method and a device for drying and subsequently cooling material webs, in particular, material webs which are printed by the offset printing process. The invention relates to a method according to the offset printing process. After contact-free drying of the printed material web, the web is guided over several chill rolls in an S or Z-shaped path. In this regard, by wetting the circumference of the first chill roll underneath that side of the material web that is cooled first, an easily splittable water film is applied between the material web and the jacket or casing of the rolls. A result of this measure is that the yet soft thermoplastic printing ink is not split during the bodily contact between the material web and this and the other chill rolls. The tendency of the material web to form waves transversely to the pass-through direction is reduced, because the splitting of the water film as a consequence of the different thickness thereof in the printed and the nonprinted and therefore highly dried regions leads to a uniform moisture distribution.
In the proposed solution according to the published German Patent Document DE 197 10 124 A1, a method and a device for controlling the temperature of chill rolls are disclosed. This proposal is concerned with a method and a device for cooling a printed or coated material web, which in particular has been printed by the offset printing process and is formed of paper. After the application of ink, the material web passes through a heating zone and is guided over a multiplicity of chill rolls in a chill-roll stand. In this regard, the flow of the cooling medium or coolant through the chill rolls of a chill-roll stand is produced by two different cooling circuits or circulatory loops at different temperature levels, and is directed over the chill rolls in a direction opposite to the travel direction of a material web.
In the structural embodiment of the last-mentioned German patent application also, the cooling-roll stand is arranged separately from the upline dryer of the rotary printing machine.
Conventional dryer/chill-roll stand configurations have separate dryer housings and separate housings for chill rolls and rewetting units, which are located further downline of the web travel plane. These housings, which are mutually separated, have a significant disadvantage in that problems occurring in one housing cause further problems in the next housing arranged downline thereof, such as, for example, lateral run-out or travel of the material web. Heretofore known cooling-roll stands require a relatively large amount of erection space and, consequently, increase the overall construction length of a web-fed rotary printing machine. In addition, in conventional cooling-roll stand arrangements of the prior art, oil condensation may occur on the surfaces of the first chill rolls of these chill-roll stands.
In view of the foregoing improvements proposed in the prior art and in conventional dryer/chill-roll stand configurations, and the problems occurring in the technical sector, it is an object of the invention of the instant application to provide a dryer with an integrated cooling unit wherein the disadvantages resident in conventional dryer/chill-roll stand configurations, such as a build-up of ink, lateral run-out or travel of the material web, and the aforementioned condensation problem are eliminated to a great extent.
Another object of the invention is to provide a dryer with an integrated cooling unit of such construction as to reduce the overall length of a rotary printing machine.
A further object of the invention is to provide such a dryer with an integrated cooling unit which avoids exposing the operating personnel of a web-fed machine to post-evaporation or after-vaporization.
Yet another object of the invention is to provide a dryer with an integrated cooling unit which permits the alignment of a folder or a folding apparatus disposed downline of the chill-roll stand to remain independent of the other rotary printing machine components.
With the foregoing and other objects in view, there is thus provided, in accordance with one aspect of the invention, a dryer for a material web having a surface to which ink is applied, including a housing subdivided into sections, through which a web travel plane extends wherein the material web is transportable, and a cooling and conditioning unit integrated in the housing, the cooling and conditioning unit having an inlet for admitting therethrough fresh air to the housing, comprising at least one chill roll in the cooling and conditioning unit, over which the material web is guidable, the at least one chill roll being disposed and the fresh air being conductable through the cooling and conditioning unit in a manner for promoting post-evaporation of solvent inside the cooling and conditioning unit, and for preventing solvent vapors harmful to operating personnel from escaping to the outside from the housing.
In accordance with another feature of the invention, the sections of the housing include a heating section, an evaporation section and a cooling section, and the cooling and conditioning unit being disposed downline of the cooling section in a travel direction of the material web.
In accordance with a further feature of the invention, the fresh air is conductable around the evaporation section to the heating section.
In accordance with an added feature of the invention, the dryer includes connecting pipes for conducting the fresh air to the heating section.
In accordance with an additional feature of the invention, hot air at a higher temperature level is conductable to the heating section, and at least one of the hot air at the higher temperature level and hot air at a lower temperature level is conductable to the cooling section of the dryer.
In accordance with yet another feature of the invention, the air is conductable within the dryer through the sections of the dryer so as to be directed counter to a web travel direction.
In accordance with yet a further feature of the invention, recycled air is exchangeable between the sections of the dryer in the direction counter to the web travel direction.
In accordance with an alternative feature of the invention, recycled air is exchangeable between the sections of the dryer in a web travel direction.
In accordance with yet an added feature of the invention, the at least one chill roll is a first chill roll of a plurality thereof over which the material web is guidable, the first chill roll being disposed near an outlet of the dryer.
In accordance with yet an additional feature of the invention, the at least one chill roll, in the interior thereof, is free of any inserts for deflecting coolant flowing therethrough.
In accordance with another aspect of the invention, there is provided a method of drying a material web that is printed on at least one side thereof and is guidable through a dryer having a housing with a plurality of sections, wherein a cooling and conditioning unit is integrated through which fresh air is admitted, which comprises disposing a plurality of chill rolls in the cooling and conditioning unit, whereover the material web is guided after passing through the sections, and conducting fresh air through the cooling and conditioning unit in a manner for promoting post-evaporation of solvent within the cooling and conditioning unit, and for preventing solvent vapors harmful to operating personnel from escaping to the outside from the housing.
In accordance with another mode of the method, inlet parameters of the material web at the dryer inlet for the material web approximately coincide with the material web parameters at the dryer outlet for the material web.
In accordance with a concomitant mode of the method, the parameters include at least one of the temperature and the moisture content of the material web.
Because the material web, such as a printed paper web, both sides of which are printed, is no longer exposed to the conditions of the surrounding atmosphere between the dryer and the chill-roll frame, the adherence of boundary layers of cold air to both sides of the material web can be prevented. In this way, air cushions between the chill-roll surfaces and the sides of the material web contacting the latter can be avoided, by which oil condensation is also eliminated. Furthermore, by the arrangement according to the invention, sooting at the dryer outlet can be avoided, because the dryer outlet is no longer connected to the surrounding atmosphere, because the chill-roll frame according to the invention of the instant application is integrated in the dryer housing. Fresh air, which is conducted through the cooling and conditioning unit that is integrated in the dryer, also contributes to the post-evaporation or re-evaporation within the combined dryer/cooling-roll frame/conditioning-unit arrangement.
In further developments of the invention of the instant application, the dryer includes a heating zone, an evaporation zone and a cooling zone, which can be separated from one another or in which the heating zone and the evaporation zone are combined with one another and are separated only from the cooling section. Arranged in each of these zones are appropriate upper and lower blowers, which recycle conditioned air, for example hot air supplied from burner units and recirculated air emerging from the nozzle bars, back to the nozzle bars, which extend through the zones of the dryer. In advantageous process-air guidance methods according to the invention of the instant application, process-air and hot-air guidance methods will be described hereinbelow which are suitable for operating a dryer according to the invention of the instant application either in accordance with countercurrent or continuous air guidance principles.
In accordance with a method of treating a material web according to the invention of the instant application, the methods of heating, evaporation, cooling and cooling on a chill-roll stand, combined with one another, all proceed in a common housing, which is encapsulated from the ambient atmosphere surrounding it. A material web entering the arrangement according to the invention of a combined dryer/chill-roll frame housing has, at the entry or inlet thereof, virtually the same entry parameters as the parameters at the outlet thereof, such as the lateral position of the web, the temperature level and the moisture content.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a dryer with an integrated cooling unit and method of operation, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: